<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>  </title>
    <style>
        body{
             background-color:#f4f4f4;/*背景色 */
            color:#444;/*前景色*/
        }
        .box{
            width: 300px;
            height:300px;
            background-color: blue;
        }
        .child{
            width: 100px;
            height: 100px;
            background-color: yellow;
            /* background-color:transparent; 透明背景*/
        }
    </style>
</head>
<body>
    <h1>测试</h1>
<div class="box">
    <div class="child">测试</div>
</div>

</body>
</html>